# Creating Right of Way Offsets

Offsets are points whose positions are specified by an offset distance and direction from another point. The offset distance displayed in the Traverse View is negative (-) for left offsets and positive (+) for right offsets.

The offset direction is dependent on the configuration of the point being offset.

• If the point being offset is on a curve, the direction of the offset point will be toward or away from the radius point of the curve.
• If the offset is at an angle point where two tangents meet, the offset direction will bisect the angle created by the two tangents.
• If the offset is along a spiral, the offset direction will be toward or away from the computed radius point for that position on the spiral.

TPC has an automatic setback tool

• If you have specific setback distances for Front, Side and Rear lot lines, you can use TPC's Lot Setbacks tool to draw setbacks in a drawing. TPC does not generate points or traverses for these setbacks, but they are simple and easy to use.

TPC makes it easy to compute offsets through the use of traverses.

• Choose the traverse that defines the boundary, centerline or other figure you want to offset.
• If you dont want to offset the entire traverse, just highlight that portion you do want to offset by dragging the left mouse button or holding down a Shift key while pressing the down arrow or page down key.
• Choose COGO | Right of Way Offsets.  See Accessing COGO.
• From the Right of Way dialog, choose [X] Left and/or [X] Right and enter the individual offset distance for each.
• Enter the type of label to give the offset points (explanation follows). If you forget how to specify an offset label, just press F1 for on-line help.
• In the Offset What box, choose the part of the traverse to create offsets for.
• Choose Save as Offsets or Save as Traverse.

## Labeling Offset Points

You can determine how the offset points created will be labeled.

• To add a prefix or suffix to the label of the point being offset, use an *. TPC replaces the * with the original point label. So if you enter *L for the left label, the left offset of point 200 will be labeled 200L.
• TPC replaces the % character with the offset distance. So if you enter *L% for the left label, the 40 left offset from point 200 will be labeled 200L40.
• To add or subtract a number, use + number or  number, as in +1000.

## Specifying an Offset Tolerance

The offset tolerance determines how close the first and last point being offset need to be in order to be treated like a closed loop. If they do not reference the same survey point but are within the specified tolerance of each other, they will be considered the same point. The figure will close and you will get a single offset instead of two, as shown below.

If the figure you are offsetting is a closed loop, the first and last points are considered to be the same point, so the offset bisects the angle at that point. If they are not considered the same point, each one will have its own perpendicular offset.

## Saving Offset Points

As TPC computes the offsets, you can save these points one of two ways as 1) offsets (like sideshots) from their original points or 2) in a new traverse.

### Save Offsets as Offset Points

If you choose Save as Offsets, TPC creates an offset point from each point being offset in the current traverse. Offset points get drawn with the side shot settings in Drawing View. You can think of an offset point like a side shot from the point being offset.

### Save the Offsets in a New Traverse

If you choose Save as Traverse, TPC creates separate traverses for the left and right points. The created traverse name starts with Left dist followed by the original traverse name for the left offset and Right dist followed by the original traverse name for the right traverse.

Saving the offsets as a traverse creates a figure or boundary along the offset. You will use this option to show setbacks on a lot or right-of-ways along a centerline.

Starting in TPC Desktop 2011, TPC insures that this traverse receives a unique traverse name. It does this by appending a unique number to the traverse name. So for example, multiple offsets from the 'Centerline' traverse will be named 'Centerline1', 'Centerline2', etc.

## Tangent-Tangent Offsets

For tangent-tangent offsets (where two tangents meet), TPC bisects the angle between the two tangenst to compute the resulting offset.

## Spiral/Curve-Tangent Offsets

For sprial-tangent or curve-tangent offsets (where a spiral or curve meet a tangent), TPC does a series of computations that insure the computed offsets point meets the required offset from both the spiral/curve and the tangent.

Look at the diagram on the right.

•  TPC first computes the Intermediate point offset perpendicular to the tangent.
• Then it computes the Bearing-Distance intersect, using the tangent bearing passed through the intermeidate point and the new radius distance from the radius point of the spiral/curve.

As a result of this computation, the resuting direction from the radius point of the curve to the computed offset (blue radius) may not exactly match the direction from the radius point to the end point of the spiral/curve (red radius).

## Curve-Curve Offsets

For curve-curve offsets, TPC does a Distance-Distance intersect using their two radius points and corresponding radii + offsets.

## Spiral-Spiral/Curve/Tangent Offsets

For offsets involving spirals, TPC relies on the Spiral Offset method you have selected from the Spiral Definitions you select in the Survey Definitions.